ydb/yql/essentials/tests/s-expressions/suites/Join/EmptyLeftJoin.yqls

(
(let mr_source (DataSource 'yt 'plato))
(let list1 (AsList 
  (AsStruct '('key1 (Just (String '1))) '('value1 (Just (String 'A)))) 
))

(let list2 (AsList 
  (AsStruct '('key2 (String '1)) '('value2 (Nothing (OptionalType (DataType 'String))))) 
))

(let keyExtractor (lambda '(x) (Member x 'key2)))
(let payloadExtractor (lambda '(x) x))

(let dictOne (ToDict list2 keyExtractor payloadExtractor '('Hashed 'One 'Compact)))
(let dictMany (ToDict list2 keyExtractor payloadExtractor '('Hashed 'Many 'Compact)))
(let joinLeft (MapJoinCore (Iterator list1 (DependsOn (String 'Left))) dictMany 'Left '('key1) '('key2) '('key1 'a.key1) '('key2 'b.key2 'value2 'b.value2) '() '()))

(let res_sink (DataSink 'result))
(let world (Write! world res_sink (Key) (Collect joinLeft) '('('type))))

(let world (Commit! world res_sink))
(return world)
)